1. Field of the Invention
The present invention relates to a trigger signal detection apparatus.
2. Related Background Art
For example, a trigger signal detection apparatus is widely used, which receives as a trigger signal a signal that represents a detection of a trouble in an external device etc, outputs a signal that stays at a high level for a predetermined time since the reception of the signal, stops the output of the high level signal after the predetermined time elapses, and outputs a low level signal or one-shot pulse. This type of apparatus has been used for such a control to stop the driving of a motor for a predetermined time when a trouble is detected and, after the predetermined time elapses, restart the driving.
However, in one of the prior art of the trigger signal detection apparatus, once a clock signal for counting the predetermined time is supplied, all of circuits in the apparatus operate all the time, so there causes a problem in that unnecessary power is dissipated wastefully.
A variety of techniques are proposed to reduce the dissipation power of the apparatus; for example, Japanese Patent Laid Open Publication No. 2002-141789 discloses a technique to decrease the dissipation power of an apparatus that detects a transiting edge position and then operates based on the detected edge position. However, Japanese Patent Laid Open Publication No. 2002-141789 does not refer to a trigger signal.
Another prior art of the trigger signal detection apparatus has performed clock gating at a stage of receiving a clock signal at necessary timing only when the clock signal is supplied, for suppressing dissipation power. However, to perform clock gating, a clock enable signal is required, so a new circuit block is inevitable to generate the clock enable signal. This has resulted in a problem in that the apparatus as a whole would be increased in size and could not effectively be decreased in costs including the dissipation power.